12V SLA Powered 15W LED Lamp



Introduction: 12V SLA Powered 15W LED Lamp

About: Autistic person who's interests include utility cycling, recreational cycling, cycling safety, electronics, gardening, Arduino, and LEDs.

This lamp uses an ATtiny84 based LED driver with a switching frequency of 78.125 kHz. The microcontroller was also programmed for monitoring the battery's state of charge which reminds you to recharge it, and turns it off to prevent overdischarging. You can power it with a 12V DC power supply if you want. This circuit can be upgraded for fan control for extra cooling, and 3A drive current for 30W operation.

Possible applications:

  • Flashlight
  • Emergency lighting
  • Work light
  • Photography
  • Outdoors activities

Update: There's a 3A driver for this lamp for 30 watt operation.

Step 1: Circuit

In the circuit that was built:

  • 150 ohm was used instead of 10 ohm for R16
  • R5 through R8 were replaced with three 1.1 ohm resistors
  • Two 100uH 2A inductors were placed in parallel
  • The heatsink fan was not installed
  • The thermistor for the heatsink was not installed
  • 3 Cree XPL LEDs were used in series

PCB Express files were uploaded in case you need to modify the circuit board.

Step 2: Upload the Code to an ATtiny84 Microcontroller

Step 3: Drill the Heatsink

For fan, cable ties, and plastic cover (if needed).

Step 4: Drill the Wood to Attach the Heatsink and the Battery

Step 5: Glue the LEDs to the Heatsink With Epoxy

Step 6: Carve the LED Lens Holders

Step 7: Hot Glue the Optics to the LEDs

Step 8: Make the Power Cable

The power cable should allow convenient charging by connecting the DC plug, charging socket, and battery connectors in paralle.

Step 9: Lamp With PCB, Battery, and Heatsink

Step 10: Instructions

  • Always top up the battery and recharge it after using it for long life.
  • Blinking red means low power.
  • Three red blinks mean going to sleep.
  • Solid red means the battery indicator is off or battery voltage is higher than 14V.
  • Red LED off means the battery is between low and fully charged.
  • Enable the battery monitor when using a battery. Disable it when using an external power source.
  • Clicking the button cycles through the brightness levels.
  • Holding and releasing the button turns it on or off.
  • Only connect the battery, SLA charger, or the circuit board's DC socket the the power cable that you made.
  • To use an external power source, disconnect the battery from the DC socket of the circuit board, and connect the external source to the socket.

Step 11: Possible Improvements

  • To make it become a 3A LED driver, you can try using an IRF9540N which can handle more power instead of the AO3401, a 5A schottky diode instead of the 3A diode, a 4A inductor, and a higher power rating or lower resistance current sense resistors. With the current design, I couldn't drive set it to 1.5A without causing overheating, and 3A without destroying the AO3401.
  • Update the code for fan control if more cooling is needed.
  • If you want to use other battery chemistries such as NiMH, Li-ion or alkaline, you can update the code. I used SLA because it was used for my bike but now it's upgraded to Li-ion. The old battery can now be put to use.
  • Use a deep-cycle battery to allow a higher depth of discharge.
  • Use a higher capacity battery for a longer run time. The battery used was 4Ah.
  • Omit the LED lenses if wide angle is desired possibly in photography.
  • Use higher CRI LEDs for photography.
  • Add a hinge to allow aiming.
  • Add a carrying handle.
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